System and method for preventing auto thefts from parking areas

ABSTRACT

A method and system to prevent auto theft from parking areas, such as airport parking lots, includes a ticket dispenser, at an entry gate, which issues a numbered ticket to each driver. The driver is advised to carry the ticket with him and not to leave it in the car. At the same time the ticket is issued, the a part of its license plate number, is automatically determined and entered into computer memory, in association with the ticket number. At the exit, the ticket is presented by the driver, read by a ticket reader, and its associated license plate data is retrieved from computer memory. Also at the exit, part of the license plate of the car is again automatically obtained and compared with the license plate data retrieved from the computer memory. In the event of a mismatch, a warning signal is generated.

This application is a division of application Ser. No. 08/607,125, filedFeb. 26, 1996, now U.S. Pat. No. 5,638,302, which was acontinuation-in-part application partly based upon application Ser. No.08/566,145 filed Dec. 1, 1995, now U.S. Pat. No. 5,568,406, issued Oct.22, 1996.

FIELD OF THE INVENTION

The present invention relates to the prevention of car theft and moreparticularly to the prevention of cars being stolen from a parking area.

BACKGROUND OF THE INVENTION

At the present time the theft of automobiles (cars) from parking areasis an important problem. "Parking areas" include shopping malls, parkinglots and other outdoor and indoor parking areas, indoor parking garages,airport parking lots and other paid and unpaid car parking facilities,gated communities (private communities) as well as military bases andother facilities where cars are parked.

Despite the best efforts of auto manufacturers, car theft devicemanufacturers and the police, car theft from parking areas remains asone of the most prevalent crimes, resulting in the loss of billions ofdollars and high car theft insurance rates in many areas. In addition,customers may fear leaving their cars in shopping malls, and otherparking lots, resulting in a loss of business to such malls.

Car manufacturers now produce cars with various anti-theft devices, suchas locked steering wheels, keys with microprocessor chips, and remotecontrol locks. In addition, various steering wheel locks and bars arewidely used. Another anti-theft system uses a radio transmitter hiddenin the car which is activated when the car is reported as being stolen.Despite these devices, car theft from parking areas is still a problem.For example, The New York Times, Feb. 6, 1996, pages B1, B4, reportsthat at the Green Acres shopping mall in Valley Stream, Long Island,N.Y., as a result of increased security, the number of cars stolen fromthat mall fell from 532 cars in 1984 to 159 cars in 1995, still anunacceptably large number.

When a car is stolen it may be reported to the police almostimmediately. However, by that time it may be out of the parking area andon its way, for example, to be disassembled in a "chop shop" or shippedabroad. The police would be notified of the car's description, i.e., "awhite 1995 Acura Legend four-door" and its license number, i.e., NewYork "JWB 123". However, the thief, to prevent being caught, mayimmediately, before he exits the parking area, switch the originallicense plates with license plates he has brought with him.Consequently, the police would not be able to detect and stop the stolencar even if they are present at the exit of the parking area when thethief drives out with the stolen car.

The issued U.S. Patents mentioned below are incorporated by reference.U.S. Pat. No. 4,947,353 uses a scanning laser, which scans at 160 timesper second, on one side of a roadway, and a vertical elongatedphotoelectric detector on the other side, to measure the heights ofvehicles. U.S. Pat. No. 5,088,827 discloses a system for measuring thewidth of a traveling object, such as a wire, being manufactured. U.S.Pat. No. 5,083,200 relates to using a linear camera for obtaining thesilhouette of a traveling vehicle to determine if it is a truck etc.,using its length and height. U.S. Pat. No. 5,381,155 uses a licenseplate reader, a speed measuring device, a data base of registeredvehicles and a variable message sign to display the names of speedingdrivers on the sign. In U.S. Pat. No. 5,066,950 two spaced-apartinfra-red beams are used to indicate the speed, length and separation oftraveling vehicles for photographing speeding vehicles.

The following U.S. patents relate to reading license plates andgenerating digital signals representing the plate numbers: U.S. Pat.Nos. 4,567,609; 4,817,166; 5,081,685; 5,136,658; 5,175,617; 5,204,573;5,204,675; 4,731,854; 4,878,248; 5,315,664; 5,425,018.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a system andmethod to identify cars which have been stolen as they exit a parkingarea. The system operates on all cars without any modification, additionor device on the cars.

A basis of the system and method is that a ticket is issued at the entrybarrier gate of the parking area, the driver keeps the ticket with himwhile shopping, visiting, etc., and the ticket is presented at the exitbarrier gate. The ticket is associated with the car, for example, bylicense plate number and a physical characteristic of the car,preferably length, color and lens shape (headlight and/or rear light).

If a thief steals a car, he would not have the ticket which matches thecar. A thief may drive a junk car into the parking area and would obtaina ticket, but the ticket would not match a car he steals and seeks toexit with. Preferably the tickets are numbered so that even if a thiefcounterfeited a ticket its number would not match the physicalcharacteristics or license plate of the car he steals. The thief cannotsteal a car and switch plates, even of the same color and model car, ashe would not have a ticket having a matching plate number. And a thiefcannot simply drive away a stolen car, as he would not have the requiredmatching ticket.

Television cameras (electro-optical sensors) are mounted at the entryand exit of the parking area to read license plate numbers. One set ofselected camera locations are on the poles on the sides of the parkingarea entry or exit road, or on overhead support structures spanning sucha roadway, or on light fixtures or stop lights which extend over theroadway.

The camera is preferably an automatically turnable camera of thespeed-variant type, producing an image of less than 40,000 pixels. Thecamera is connected to a digital computer, preferably a special computer("processor board") having fast digital processing chips (DPC) which hasbeen programmed by software. The computer performs two functions. First,it "reads" the license plate number, preferably by a template matchingsystem. Secondly, it may also be used, optionally, to help identify thecar's model and color, again preferably by a template matching systemwhich relies primarily upon the shape and spacing of the car'sheadlights and rear lights.

The preferred physical characteristics of the "target car" (the carentering or leaving the parking area) are its color, length and width.The length and possibly the width is measured. If a target car'smeasured length is not the same as the length retrieved from the ticket,or computer system memory (data base), it may be a switched ticket orcounterfeit ticket and the car may be stolen. A warning signal isgenerated so that an exit gate is not raised and so that the target carmay be stopped by a police officer.

The preferred system to measure car length employs a laser rangefinderpointed at the front of the car and a second laser rangefinder pointedat the back of the car, when the car halts, at the entry, for the driverto reach for a ticket. The length of the car is calculated, by acomputer system, from the results obtained from the two rangefinders.

A less preferred system to determine a car's length uses a series of,for example 250 photoresponsive sensors in a line, spaced one inchapart. The car's length is measured by how many of the sensors areaffected by the car.

Another system to determine the car's length consists of two spaced, orangled, light beams, for example, laser or infra-red beams. The car'sspeed is determined by the time that elapses from the front of the carinterrupting the first light beam until the front of the car interruptsthe second light beam. The length of the car is automatically derivedfrom the computer, from the length of time each beam is interrupted bythe car, combined with that car's speed.

Although one embodiment uses a license plate reader (LPR) the system andmethod may be implemented using only the physical characteristics ofcars, including length, width, color and lens array. The system, withoutan LPR, would detect almost all stolen cars. In this case a ticket isassociated with, for example, car length and color. In almost all casesthis is sufficient to identify a car. However, a car will occasionallyhave an object protruding from its trunk, for example, which the ownerbought in the mall, so the length will not be the same at entry and atexit. In that case the driver may be asked for identification. Inaddition, the color would not be an accurate guide if it is snowing; inwhich case the color reader may be shut off.

The "characteristics" of a vehicle include its license plate number,length, width, color and shape, especially the shape of its front andrear lenses.

The system, in the event of a mismatch (the ticket does not match thecharacteristics of the car) generates a "warning signal". For example,the warning signal causes the exit barrier gate not to lift. The warningsignal may also be a bell or buzzer which is sounded, or a display whichis illuminated, at a gate house, office or security force vehicle.

If a customer loses his ticket, or the computer system indicates thatthe ticket which is presented does not match the car, the driver wouldbe asked for identification. Preferably the required identificationwould be the car's registration, having its license plate number andowner, and a "photo ID" (photograph identification). Such identificationmay be shown to a guard at the exit gate, to personnel at an office, orplaced on a surface under a TV camera connected to a monitor at afacility office. The guard, or office, may lift the exit barrier gate bya signal to that gate.

The duplication of two ways to identify a car, for example, the licenseplate number and car length, is to avoid "false positives" in which acar is incorrectly identified as being stolen. If only license platesare used, with presently available technology, at best 1 out of 100 carswould be incorrectly identified as stolen (ticket not match partiallicense plate number). It is preferred that a car be considered notstolen if either the partial license plate number or the length detectedat the exit gate match the ticket. Using that alternative matching, itis believed that less than 1 out of 10,000 cars would be incorrectlyidentified as stolen and its driver asked for identification.

This system and method does not require an attendant at the exit. Ifthere is an attendant, it does not require his diligence or attention inthe identification of cars. Any system that would require an attendantto identify cars would be unreliable as he may be inattentive or busy.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objectives and features of the present invention will be apparentfrom the following detailed description of the invention, taken inconjunction with the accompanying drawings. In the drawings:

FIG. 1A is a block schematic diagram and FIG. 1B is a flow diagram ofthe preferred embodiment of the present invention;

FIGS. 2A and 2B are perspective views of mounting systems for the videocameras and for the double light beam system, which is an embodiment ofa car length measurement system;

FIGS. 3A and 3B are perspective views of another embodiment of a carlength measuring system and of a car width measuring system,respectively;

FIG. 4 is a schematic diagram of the first embodiment of the car lengthmeasurement system of the present invention; and

FIG. 5 is a front view of a ticket dispensing machine.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, the system of the present invention includesa first and a second optoelectric video camera 9 and 10 to read thealphanumerics on vehicle license plates. The cameras 9 and 10 aremounted on support structures 11A and 11B above the entry and exitroadways 12A and 12B to a parking area, although alternatively they maybe mounted on a post on the side of the roadways. Camera 9 is positionedto read the license plate on the back of the target car at the entrance,and camera 10 is positioned to read the license plate on the back of thetarget car as it exits the parking area. For additional security, fourcameras may be used on a single lane entry and single lane exit to readboth the front and rear license plates, in those states requiring bothfront and back plates.

The camera systems 9 and 10 take an image of the license plate and thenconvert the image of license plate numbers into a conventional ASCIIdigital code. A preferred camera is being developed by VisionApplications Inc. (Allston, Mass.). That camera is utilized in U.S. Pat.Nos. 5,175,617 and 5,204,573. It produces a logmap image from aspace-vibrant sensor. The camera is preferably a CCD image sensor(Charge Coupled Device) having 192×165 pixels (31,680 total) with a lensassembly of under 0.5 ounce, the image sensor being mounted on aspherical pointer motor.

The camera systems 9 and 10 read the license plates of all the vehiclespassing within their area. Each camera 9 and 10 is electricallyconnected to a specialized computer processor board 13 which convertsthe alphanumerics of the license plates of vehicles to a digital ASCIIcode which is transmitted as data streams 16A from camera 9 and 16B fromcamera 10 to computer system 15. Each camera and its processor boardconstitute a "camera system"; although with storage of image frames asingle processor board 13 may be used for both cameras 9 and 10. Thatconversion uses algorithms and template matching techniques used incharacter recognition systems. The license plate characters, in onejurisdiction (state), would be of only one font, making their conversionto digital signals relatively simple. Preferably the computer processorboards 13 are physically mounted on the same support structures 11A and11B as the cameras 9 and 10. However, a single computer processor board13, with a suitable time-sharing buffer memory, may be used for aplurality of 2-4 cameras.

Preferably the driver is issued (dispensed) a ticket at the entry to theparking area. A suitable ticket issue machine 20 is associated with anentry gate so that the driver must pull a ticket from the ticket issuemachine in order to lift the entry gate.

A suitable system pre-prints the tickets with a bar code, either in anumber sequence or a semi-random or random number sequence. The ticketdispenser reads the number of the ticket it issues, using a bar codereader, and associates that number (in computer system memory) with thephysical information (length, color etc.) about the car for which theticket is issued. A less preferred system is to print the physicalinformation, in bar or other code, on the ticket. If the physicalinformation is printed on the ticket, the tickets may be counterfeited;although the system may be simpler. A suitable car code ticket issuingmachine which prints and encodes as the tickets are issued is Series90-4 (TM) from Parking Products, Inc., Willow Grove, Pa. A suitableticket issue machine, having a bar code reader (bar code scanner) whichcan read pre-printed bar code on tickets, is Model SP (TM) of StanleyParking Systems, Farmington, Conn. 06032. Both Parking Products andStanley Parking sell suitable electrically operated entry and exit gatesand "loop detectors". A vehicle loop detector is a coil of wire embeddedin the roadway in front and after a barrier gate to trigger a controllerthat a car is located above the loop. A loop detects the presence of acar, the ticket issue machine automatically issues a ticket, thedriver's removal of the ticket causes the entry barrier gate to raise(open) and the car's passage over the loop after the entry gate causesthe gate to be lowered (closed).

In a mall or other free parking area, the ticket would be free. However,in an airport parking area, parking garage or other fee-based parkingarea, the ticket may be the same ticket which is presently used forrevenue parking. Alternatively, the ticket may contain additionalprinted information. For example, if a presently used fee-based systemprints the date and time of entry on the ticket, in bar code or inalphanumerics, the date and time without modification may be used as theticket's number. That number, along with data representing the selectedcharacteristic of the vehicle, is then associated in computer systemmemory for later retrieval. In addition, that number is read, preferablyby a machine, at the exit. For example, if the ticket is printed in barcode the driver, at the exit, would insert the ticket into a bar codereader.

The tickets are preferably of conventional size, either 2"×4" or21/2"×6" (SP and SPC) and 9-point ticket stock.

A sign at the entry gate reads "Please Take Ticket And Keep It WithYou--Not In The Car".

An alternative license plate number reader, which is commerciallyavailable, is made by Racal Radio Limited, 472 Basingstoke Road,Reading, Berkshire, England. It reads license plates from a recordedvideo image (digital image grabber) using pattern recognition techniquesand neural networks. The neural networks are trained on a large numberof sample characters. That system, called "Talon" (TM), recognizeslicense plates in about 0.25 seconds; reads plates on cars traveling athigh speed; data can be locally stored or transmitted via land-line orradio to a remote site; and reads plates directly from a video imageusing programmable DSP (Digital Signal Processing) hardware. The systemincludes a camera, lighting, plate recognition unit (PRU) and keyboard.It displays, among other things, a copy of the video image and a rollinglist of license plates, the list output being via a standard RS 2343interface.

Real time license plate recognition (LPR) systems are also availablefrom: Gevis GmbH, Innstrasse 16, A-6240 Radfield, Austria(identification time 0.5-0.7 seconds); Perceptics, Knoxville, Tenn.;Imaging Systems, Burlington, Mass. 01803; and are being developed byZamir Ltd., 17 Hauman St., P.O. Box 53426, Jerusalem 91533, Israel; andComputer Recognition Systems Ltd., Fishponds Close, Wokingham, BerksRG11 2QA, England.

The following U.S. Patents have issued on various systems relating tolicense plate recognition (LPR) and are incorporated by referenceherein: U.S. Pat. Nos. 5,425,108; 4,787,248; 5,136,658; 5,175,617;4,817,166; 4,731,854; 5,204,675; 5,204,573.

It is important that the camera system and measuring system detectalmost all the cars in its area and that the license plate numbers beread with accuracy. Since the presently available license plate readersoperate at no more than 90% accuracy, this presents a problem. Apossible solution is based on reading only 3 or 4 alphanumerics andvoting. For example, the entry camera 9 makes two readings of the rearplate,those readings being the left 3 alphanumerics and the right 3alphanumerics. Similarly, the exit camera 10 makes two readings of therear plate, the left 3 alphanumerics and the right 3 alphanumerics. Anacceptable result would be a match between one rear plate reading (leftor right) and one corresponding rear plate reading (left or right).

The cameras and computer systems may be arranged in different ways toobtain higher accuracy license plate reading results. Some suitablearrangements are:

One entry camera takes pictures of the front plates and a second entrycamera takes pictures of the rear plate. Similarly, the exit cameras andobtain images of the exit target car's rear and front license plates,respectively. All four cameras are connected to a high-speed licenseplate reader, such as a RACAL, which can analyze a plate in 250 ms(milliseconds). Each camera takes one frame for analysis, for a total of4 frames, which are analyzed by the computer in sequence, for 1 secondtotal of analysis. The four results are compared. An acceptable readingconsists of one match from the entry and exit cameras.

A false positive (incorrect plate reading) is highly unlikely if oneassumes that the reading errors are random. In theory, assuming that the10% error on each reading is random, at least 98% of the plates would beread and almost no accepted results would be incorrect.

The computer system preferably has its own data base. For example, usinga conventional hard disk (Winchester drive), 10,000 license platenumbers and their associated information (length, width, color, owner'sname, etc.)., about 100 bytes per plate, is a data base of only 1million bytes (1 megabyte). These may be stored in a writable magneticdisk having under 20 ms retrieval time. New license plate informationmay be added at any time using a keyboard or over a communication line.

Presently suitable computer systems are available from Stanley Parking("facility management computer system") and Parking Products (TPC-300)as well as PCs (Personal Computers) from IBM and others.

The system does not require a computer system to keep track of ticketnumbers if a car's identification is printed on the ticket. However,this system, although relatively simple, is subject to thecounterfeiting of tickets. In this system the car's license plate andphysical data (length, color, etc.) are printed on the ticket, in barcode or other code, by the ticket issue machine. That ticket is read, atthe exit, by a ticket reading machine. A simple computer system at theexit attempts to match the data read from a ticket with the dataobtained by the sensor at the exit gate.

Even if by chance the thief has stolen a car and used the registeredplates of a car of the same length, or close to that length, if thedetected color does not match the registered color the plate is likelyto be a switched plate.

With this system mistakes may occur, for example, because a car iscarrying an object which protrudes from its trunk, increasing itsapparent length.

The preferred car length measuring system uses, at each of the entranceand exit, a first laser rangefinder whose laser beam is directed at thefront of the car and a second laser rangefinder whose laser beam isdirected at the back of the car The distance from each of therangefinders to the car is obtained and a computer system calculates thelength of the car from those measurements.

The preferred rangefinder is a laser (Light Amplification by StimulatedEmission of Radiation) rangefinder which uses an intense, directional(narrow), coherent, monochromatic beam generated by a semiconductor (ordiode) laser in the infrared or visible (red) range. The distance ismeasured by the time it takes a pulse (pulse burst) of the laser beam tothe car (target) and back. The distance is sufficiently short, less than20 feet, so the car will reflect the laser beam back to the laserphotoresponsive detector proximate the laser.

In a more sophisticated system a third laser rangefinder measures thedistance from the ticket machine to the car. Generally that distancewould vary, at most, about four feet, the length of an arm. The tworangefinders are then controlled to pivot to pick out points on the car,for example, one foot, beyond that distance. This will ensure that thelaser beams at the entrance and exit are reflected from the same pointson the car, to avoid problems due to the curve of the bumpers or sheetmetal. Preferably the laser beams are directed at the car's bumpers,which are at the same height for most cars.

FIG. 4 shows a laser rangefinder system to measure car lengths. One suchsystem is preferably used at the entrance, i.e., entry barrier gate, anda second system, of the same type, is preferably used at the exit, i.e.,exit barrier gate. A laser 60 produces a laser beam 61 which is directedat the back bumper of a car 62. A portion of the beam is reflected andreturns to be sensed by photodetector (laser detector) 63. Similarly asecond laser 64 produces beam 65 which is reflected by the front bumperof car 62 and is sensed by photodetector 66. The imaginary line 66between lasers 60 and 64 forms two imaginary right angle triangles. Thelaser photodetectors 63,66 are connected to a computer system which usesappropriate trigonometric formulae (or a look-up table) to compute theline segments 66A and 66C. The line segment 66B is computed from lengthof 66-(66A+66C)=66B, where 66B is the measured length of the car.

A more sophisticated system uses a third laser rangefinder 70, havingbeam 71 and photodetector 72, which measures the distance between theticket machine, or other fixed point, and the side of the car. Thelasers 60 and 64 are mounted on pivotable tables and are pivoted so thattheir beams strike the car at almost the same points at the entry andexit, to avoid any errors arising from the curvature of the car body orbumper.

A suitable pulsed time-of-flight laser rangefinder in the HAWK (TM) isavailable from Schwartz Electro-Optics, Orlando, Fla. 32804. It providesa digital output and has a ranging capability of 10-80 feet withplus-minus 1-inch accuracy and, for the present application with a rangeof 10-20 feet, may have an accuracy of plus-minus 0.5 inches. Analternative laser rangefinder, which is slower but less expensive, isModel C5148 and daylight point finder Model C53149 from EdmundScientific, Barrington, N.J. 08007.

A less expensive system may be envisioned using only a singlerangefinder. For example, a single rangefinder 60 sends its beam 61, for1/10 second, and then a mirror is interposed to send the beam fromrangefinder 60 along line 66. A mirror, at the position of rangefinderlaser 64, replaces rangefinder laser 64 and directs the beam 65 to hitthe front of the car for 1/10 second. In this way the distances of beams61 and 65 are measured using a single laser rangefinder. If desired, thepath of line 66 can be enclosed in a pipe or tube to prevent blockage ofthe beam long line 66.

A single laser may be used for the entry and exit if the entry and exitare next to each other. The same laser rangefinder may be pivoted todirect its beam either right--as seen from above--for entry, or left,for exit. A pivotable mirror, at the location of laser 64, may be usedto direct the left beam 65 and a corresponding right beam, at differenttimes.

Inexpensive range finders ($200-$400) for hunters are made by Bushnell(Lytespeed-TM) and Brunton (Laser 70) and may be adapted for thispurpose, although with a loss of accuracy compared with a more expensivesystem. If the system is less accurate, for example, 1-inch plus-minusat entry and exit lasers, then cars which are within a 4-inch band inlength would pass the length measuring matching procedure. A stolen car,on a random basis, may have abut a 3-5% chance of not being detectedwith a less accurate system.

The less preferred system for measuring car lengths is the directmeasurement system shown in FIG. 3A. This system is particularly usefulwhen cars are moving slowly or are fully halted, for example, an entryor exit gate. In this system a series of light beams 50a-50n (where n isfrom 50 to 250), preferably laser beams or infra-red beams, are alignedin a line along the direction of traffic and in the center of a trafficlane. Preferably the beams are spaced 1 inch apart (2.54 cm) and thereare at least 50 beams and preferably 250 beams. A car will break(interrupt) the number of beams according to its length. For example, a120-inch (304.8 cm) car will interrupt 120 beams, spaced 1 inch apart(2.54 cm). Each beam has a reflector 51a-51n also spaced 1 inch (2.54cm) apart, aligned in a row and fixed beneath the beam generators on theroadway. The reflectors 5la-51n each reflect a beam back to aphotoresponsive transducer. Preferably also second lines of beams50a'-50n' and reflectors 51a'-51n' are used, spaced about 3 feet frombeams 50a'-50n' and parallel thereto. Alternatively, instead of usingreflectors, the line of photoresponsive transducers (photodetectors) maybe located on the roadway and a single laser, or infra-red generator,may be positioned overhead which sweeps its beam rapidly, i.e., 1/100second, back and forth over the line of photodetectors. This system ofdirect measurement of car length does not require any measurement ofspeed.

This system of direct measurement using multi-photodetectors ispreferably also used to measure the width of cars. This widthmeasurement system is also preferably used with the double-beam systemof FIGS. 2A and 2B, and the multi-beam system of FIG. 3A, to provide carwidth information. As shown in FIG. 3B a line of light beams 53a-53n,one inch apart (2.54 cm), at least 20 beams and preferably 200 beams,and reflectors 54a-54n on the roadway are aligned perpendicular to theflow of traffic, i.e., across a traffic lane. For example, if 60 beamsare interrupted the width of the car is 60 inches (152.54 cm).

Another method of obtaining the length of the car is to use two lightbeams A and B, FIG. 2B. Each beam is directed at opposite ends of aspace which becomes occupied by a moving car, i.e., each beam, insequence, is broken by the car. If the two beams are A and B, as shownin FIG. 2B, the front of the car will break (interrupt) beam A and thenbreak beam B. Each beam acts as a switch which is "on" (unbroken) or"off" (broken by the presence of a car).

The distance between beams A and B is exactly determined and known.Preferably it is somewhat longer than the longest vehicle sought to bedetected. For example, the space between beams A and B is set at exactly22 feet (FIG. 2A) (9.6096 meters). The time it takes the front of thecar to first break beam A and then break beam B is measured by the speedof the car. A car traveling at 60 mph (miles per hour) (96.3 km. perhour) travels at 88 feet/sec or 1056 inches/sec (2682.24 cm/sec) and thetime from beam A to beam B is 0.947 milliseconds. Once the speed of thecar is derived, its length may readily be automatically computed, usingthe timing information from the "on" and "off" of beams A and B.

Preferably the speed is determined from the average speed of the frontand back of the car, as the car may be accelerating or deceleratingbetween beams A and B. The speed of the front of the car is the timefrom beam A being off to the time beam B is off. The speed of the backof the car is the time beam A goes from off to on to the time beam Bgoes from off to on. Those two speeds are averaged to arrive at "averagespeed".

At any one average speed, the longer the time period the beams A and Bare off, the longer is the length of the car.

The length of the car is preferably the time beam A is off averaged withthe time beam B is off, i.e., "average time beam interrupted". Theformula to determine car length is as follows: ##EQU1##

At 60 mph the difference between a 100-inch long and a 101-inch long caris 0.95 ms. The computation may use the formula, as above, or may use alook-up table stored in computer memory. The look-up table preferablyhas mph from 1 to 120 and average times corresponding to lengths from 80to 250 inches.

The beams A and B each may consist of three, or more, separated beams.The purpose of these multi-beams is to insure that cars are detectedalthough they are not in the center of the lane and to insure operationin the event one beam is disabled. Preferably the beams are separatedsideways (perpendicular to the direction of traffic) by about 2 feet(0.9144 meters). The shortest length measured by the separated beams istaken as the measured length, as the longer measures may occur becauseof spare tires on the back of some vehicles or items protruding fromtheir trunks. In operation, preferably the first of the beams, A1, A2and A3, and then B1, B2 and B3, which is interrupted, is taken as thesignal source and the other output signals are not used.

Preferably the beams are laser beams from lasers 40 mounted on anoverhead structure of the type shown in FIG. 2A. An alternative mountingfrom a light fixture or stop light is shown in FIG. 2B. In thisalternative the lengths of various models should be obtained byexperimentation. The beams are reflected back, from reflectors 41 fixedon the roadway, and detected by photoresponsive transducers 42(photodiodes or phototransistors) next to the lasers on the overheadstructure. To avoid the adverse effects of sunlight, headlights, etc.,each laser may be pulsed with a distinctive digital pattern or code sothat amplitude effects may be lessened. Alternatively, infra-red beamsmay be used, which would also preferably be pulsed with a suitablepattern or code. If the target vehicle is accelerating or decelerating,the speed may be too uncertain and the length measurement distorted.Consequently, it is preferred that if the speeds as measured by beams Aand B differ by more than 2 mph (3.22 km/hr) the data as to that vehiclenot be used.

It is optional to identify a second and third physical characteristic ofthe target vehicle. For example, if the primary physical characteristicis length, the second physical characteristic may be width and/or color.Alternatively, for a simple and inexpensive system, only the car's colorneed be measured. A system to detect color preferably uses a colorluminance meter and a timed Xenon flashing light to illuminate the car'sarea whose color is to be measured. For example, a light beam is shinedon the car's side and its reflection is viewed by a color luminancemeter having three photoresponsive transducers (photodiodes orphototransistors). A suitable color filter, for example, standard narrowband optical red, green and blue filters, such as Green No. 342C, RedNo. 185C and Blue No. 280C, is mounted in front of each photoresponsivetransducer to indicate if the car is, for example, blue, green, redblack, white, etc.

A preferred color luminance meter system would use a light beam toilluminate a spot on the car's side, hood or roof and a luminance meterwhich subtends a 1.0 degree cone. The color data is generated inchromaticity x, y and z coordinates and may produce at 256 digital colorindications, each being a mix of x, y and z coordinates. For example, anacceptable range (band) which is considered a match of the colors of thetarget car would be ±5% of each of the x and y coordinates. As anexample, on a scale of 0 to 1 for each of the x and y coordinates, ifthe measurement of the target car at the entry is x=0.10, y-0.16 thereis a match. But if the measurements of the chromaticity of the car'spaint at the exit are x=0.15, y=0.12, there is a mismatch and a warningsignal would be generated. A suitable color luminance meter is the"Chroma" TM from Minolta, and a less expensive alternative is a colorilluminance meter, such as the "xy1" TM also from Minolta, whichproduces a digital ASCI code output.

Even in the event of a snowstorm, the optical meter to detect colorwould not have to be deactivated, if the car's side door is viewed bythe color meter.

As shown in FIG. 5 a ticket dispenser 100 at the entry area ispositioned next to car door 101 whose window 102 is down. A flashablexenon light 103 is mounted on the ticket dispenser and is triggered toflash, for example, by the driver pulling the ticket from dispenser 100,or by a loop detector. The light 103 illuminates an area 104 on the cardoor 101 with its light beam 105. That area 104 is viewed by color meter106 which measures the car door's paint color, i.e., determines its(x,y) chromaticity coordinates. Generally the car door 101 will be only1-3 feet from the color meter 106 (calorimeter) and the car fullystopped, so that a reasonably accurate reading may be made in less thanone second when the light is flashed. The flash "on" period extendsthroughout the color measurement period.

The color measurement system at the exit is the same as is shown in FIG.5, except the lamp and color meter are mounted on the side of the ticketreader.

In the case of various models the lengths are the same or very close toeach other. For example, in 1995 models the Chevrolet Monte Carlo is200.7 inches (509.8 cm) long and the Chevrolet Lumina is 200.9 inches(510.3 cm) long; the Dodge Intrepid is 201.7 inches (512.3 cm) long;Eagle Vision 201.5 inches (511.8) long and the Chrysler Concord 201.5inches (511.8 cm) long; the Buick LeSabre is 200.0 inches long (508 cm)long and the Oldsmobile 88 is 200.4 inches (509 cm) long; the BuickSkylark is 189.2 inches (480.6 cm) long and the Oldsmobile Ciera is190.3 inches (483.4 cm) long.

It is also possible to use a number of processing boards at each camerainstallation to increase processing speed. For example, if 4 frames(from 2 cameras) are to be analyzed to read license plate numbers, 4processor boards may be used simultaneously, one for each frame.

In the preferred embodiment set forth above, a physical characteristic,preferably length, is measured for the target vehicle.

The width of the car bodies varies less than their lengths and is lesshelpful than length distinguishing one car from another. However, carwidth in some cases is an important guide in distinguishing car modelshaving about the same length. For example, in 1995 car models thefollowing cars are about (with 1 inch plus and minus) 186 inches inlength:

    ______________________________________    Model           Length  Width    ______________________________________    BMW - 5 Series  186     69    Chevrolet Astro 187     78    Chrysler Cirrus 186     71    Chrysler LeBaron Conv.                    185     69    Dodge Avenger   187     69    Dodge Stratus   186     71    GMC Safari      187     78    Honda Odyssey   187     71    Hyundai Sonata  185     70    Mercedes-Benz E-Class                    187     69    ______________________________________

In this example the width helps in the cases of the Chevrolet Astro andGMS Safari; but the other cars in this group have a width in the rangeof 69-71 inches. Eight models in this group have a length of 185-187inches and a width of 69-71 inches. So another method must be used todistinguish between the eight models in this group.

A template matching procedure may preferably be based on the followinganalysis of the two frames of the car's image. One image is of the frontof the car and the second image is of the rear. The two images willemphasize the reflection from the glass and/or plastic front and rearlight lenses. The size, location and shape of such lenses are oftencharacteristic of a car model. Also, since the edges are known, thecamera will center itself along the center.

A car's lenses are generally distinctive and, at night, would preferablybe illuminated by a flash of infra-red light. The headlight lenses are(i) symmetric, so only the left headlight lens (or the right) need beimaged and analyzed, and (ii) at the front of the car at a certainheight. A picture of the front of the car would show that its headlightlens is located within back about 10 inches from the front of thebumper. Preferably the car's headlight lens is compared to theheadlight's lenses of cars of the same length (within 1 or 2 inches plusand minus) so that comparison may be of, at most, 10 headlight lenses.Various pattern recognition and template matching systems may be used,for example, the system of U.S. Pat. No. 5,175,775, incorporated byreference.

Often the car's logo is at its center, either at the front of the hoodor on the trunk cover (boot). The logo can be "read" by the same type ofprogram as the license plate character reading program. It is estimatedthat there are about 200-300 models for a five-year period, each ofwhich may be distinguished primarily by its length and secondarily byits light lenses and logos.

In one embodiment of the present invention a historical record is madeat each camera system of all the identifications of cars, by model(length and light lenses), color and license plate and time. Forexample, if 50,000 cars pass one camera system each day, it will recordand retain for 30 days their license plate numbers, models and colors,so that any car may be traced. For example, if a car is stolen and itscorrect or its switched (false identification) license plate number isknown, then the camera systems may be interrogated, for example, over atransmission line, if that plate number is on their record. If so, thecamera system reports its own location and the time it viewed that platenumber to a central police facility.

At a very busy traffic entry or exit a car may pass each second. 21,600cars may pass an hour or 250,000 cars a day (reduced traffic at night).If each license plate and related data (time, date, location, etc.)comprises 20 bytes, each camera system would generate 5 million bytesper day.

In regard to color it is preferable that there be only 3-10 categories,for example, red, white and other (black, green, blue, etc.). It may bedifficult to detect an exact color because it may rain or snow betweenthe time the car enters the parking area and its exit.

When a match is not found, the license plate number and associatedinformation (car length, model and color) may be broadcast by localradio transmitter 21, mounted on support structure 11, to security orpolice cars in the area. A suitable broadcast system would entail atwo-way digital communication system using microwaves in the 2.5gigahertz band.

In addition, or alternatively, the information may be transmitted bymeans of a radio paging network. The parking area security cars wouldhave receivers mounted on their dashboards which would pick up thetransmitted information and either display it on a CRT (Cathode RayTube), synthesize the data into voice, or print the data. Theinformation about the stolen cars may also be displayed on a CRTsituated on the dashboards of police cars.

Preferably the digital data format information is converted to voiceinformation by a conventional data-to-voice synthesizer 20.Alternatively, or in addition, it may be broadcast as a data stream andconverted to a print-out by a data to alpha-numeric printer in thepolice cars.

Although various ways have been described to measure a car's color,length, width and its license plate numbers, other ways are within thescope of the present invention. For example, car length may be measuredby two digital still cameras, such as Cascio QV-10 LCD Digital Camera,positioned above the ticket dispenser and ticket reader. The output isformatted with distance markers, on the picture, which correspond todistances on the ground.

Also, the tickets may be magnetic stripe cards, or punched tickets, orother types of coded tickets.

What is claimed is:
 1. A method of warning of theft of vehicles from avehicle parking area having an entrance and an exit, the methodcomprising:(a) at the entrance, automatically machine sensing acharacteristic of the vehicle as it enters the parking area; (b) machinedispensing a ticket to the driver of a vehicle at the entrance; (c)machine recording data representing the obtained characteristic inassociation with data representing an identification of the dispensedticket; (d) at the exit, machine reading the ticket and retrieving thedata representing the vehicle characteristic associated with the ticket;(e) automatically machine sensing the characteristic of the vehicle atthe exit; (f) automatically, in a computer system, comparing thecharacteristic sensed in (e) at the exit with the characteristicobtained in (d) derived from reading the ticket; and (g) in the event ofa mismatch, generating a warning signal.
 2. A method as in claim 1 and,at the entrance, informing the driver to retain the ticket with himwhile the vehicle is parked in the parking area.
 3. A method as in claim1 wherein the ticket has a printed number thereon and machine readingthe printed number and entering the machine read number into computermemory before the ticket is dispensed.
 4. A method as in claim 1 andmachine recording the obtained characteristic in (c) by printing theticket with the sensed characteristic before the ticket is dispensed tothe driver.
 5. A method as in claim 4 and in step (d) machine readingthe ticket to obtain the data representing the characteristic printed onthe ticket.
 6. A method as in claim 1 and numbering the ticket before itis dispensed and machine recording the obtained characteristic in (c) byentering the characteristic into computer system memory of a computersystem.
 7. A method as in claim 6 wherein numbering the ticket is byentering a time so that a time is at least part of the ticket number. 8.A method as in claim 1 and machine reading the ticket to obtain a ticketidentifying number printed thereon and retrieving data representing thecharacteristic of the vehicle sensed at the entrance from computersystem memory based on the read ticket identification number.
 9. Amethod as in claim 1 and printing a number on the ticket before it isdispensed and entering the printed number and the vehicle sensedcharacteristic into computer system memory in association with eachother.
 10. A method of warning that vehicles are being stolen fromparking areas, comprising:(a) machine reading a license plate number ofa vehicle at an entry area of the parking area using an electro-opticallicense plate reader; (b) associating data representing the vehiclelicense plate number with a ticket; (c) dispensing the ticket, at theentry area, to the vehicle's occupant; (d) machine sensing the samelicense plate number of the vehicle at an exit area of the parking areausing an electro-optical license plate reader; (e) reading the ticket atthe exit area; (f) attempting, in a computer system, to match thevehicle license plate number sensed at the exit area with the datarepresenting the characteristic associated with the ticket; and (g) inthe event of a mismatch, generating a warning signal.
 11. A method as inclaim 10 wherein reading a characteristic, at the entry area and exitarea in steps (a) and (d) is performed by a license plate reader whichreads at least three alphanumerics of the vehicle's license plate.
 12. Amethod as in claim 11 wherein the entry area has an entry barrier gateand dispensing the ticket activates lifting of the entry barrier gate.